一质点作简谐振动<img src="https://nimg.ppkao.com/2019-05/wuacheng/2019051717124824709.jpg?sign=849fb8e6cda4292831fb190ee804459c&t=62d745de" />cm。某时刻它在<img src="https://nimg.ppkao.com/2019-05/wuacheng/2019051717125673244.jpg?sign=9208256c09d73b5999f20dcd6a1422a7&t=62d745de" />cm处，且向X轴负向运动，它要重新回到该位置至少需要经历的时间为（）<br /> <img src="https://nimg.ppkao.com/2019-05/wuacheng/2019051717130453482.jpg?sign=f063408e4de197cfa633e96b9fcb5e78&t=62d745de" />